Study of the laser ablation and flow characteristics for generating nano-particles

Nano-particles possess unique characteristics of the optical, electrical and mechanical properties. Many efforts have been made on the fabrication and characterization of nanoparticles during the recent decades. Various techniques such as physical and chemical condensations with laser ablation have been successfully adapted to synthesize nano-particles. One of the reliable methods for producing nanostructure materials is the gas-phase condensation process. During the evaporation and condensation processes, vapor has been cooled down and results in the formation of nano-particles by nucleation, condensation and coagulation. Substrate materials could be heated by various heating sources such as laser beams. In this study the synthesis of metallic nano-particles by evaporation is generated by a laser irradiated on a metallic target with a rapid condensation in a jet flow condenser. In the simulation analysis of local ablation phenomenon in gas plume, which was induced by laser ablation, small particles with narrow distributions were expected in the experiment. In order to understand the formation mechanism of the nano-particles for broader applications to the mass production, this study is going to apply the computational fluid dynamics (CFD) software and numerical method to simulate the formation of particle/flow/plume under the laser irradiation. The flow analysis is used to investigate the process design in a macroscopic view, furthermore the plume particles removed by a swirling flow nozzle in laser ablation was characterized with numerical and experimental approaches. The swirling flow was simulated by RNG? ?k{cyrillic}-? turbulent model. The gas flow passed through a specifically designed swirling flow nozzle and impinged on the substrate with various inlet velocities. The trajectories of the plume particles with nano-scale diameters in the flow field were calculated and compared with the flow visualization in the experiments. The results show that the velocity distribution of the swirling flow on the substrate was significantly affected by the swirling strength of the flow. It shows that the plume particles were removed efficiently and the surface roughness was significantly reduced by the implementation of swirling flow in laser ablation.